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Saw blade slow down

10-05-2008, 09:35 PM

I have a lightly used Ridgid table saw and while cutting the other day the blade just slowed down and now barely comes on and does not turn. The motor just hums. I had the capacitors tested (motor start and motor run) and they are still good. The man at the shop said the switch is probably bad but wouldn't it not turn on at all if that was the case? I can't find my receipt to take it to have it repaired so I am trying not to spend too much $. Any advice out there?

Comment

Check the horsepower rating on the wall switch before you go that route. With motors the amperage rating is not what you look at, that is for resistive loads only, it is derated significantly for inductive loads.

The problem could be the centrifugal switch in the back of the motor that switches between the start and run capacitors, if the motor hums then the start capacitor is either bad or the centrifugal switch is not making contact. First step is to blow out the motor with compressed air, second is to disassemble the motor and diagnose the internal problem.

Comment

If when you flip the power switch the motor growls, then that's (power switch) not the problem. As WB said it could well be the starting switch inside the motor. Does your table saw have a belt drive where the motor is behind the table? If yes, using care to note the wiring connections, you may want to remove the motor and take it to a motor rebuilding/repair shop for testing and repairs. Sometimes blowing them out can really help. In addition a few fast light taps with a rubber hammer can free up a stuck starting switch.

Question: Was the table saw running then lost power and came to a stop with the motor growling, or is it a case where you stopped it and now can't get it to restart?

Question 2: What model is your table saw? If you can't find the name plate see the two pictures. Is it like the left or the right one?

Comment

This may sound silly, but:
What else is on the electrical circuit as your table saw?

I had an unusual occurrence with a 120VAC plasma cutter that would quit for no reason. I then plugged it into a different outlet "on a different circuit breaker" and it ran just fine.

Most table saws require a higher current during start up [in-rush current, or surge current] then settle down to its normal running speed current draw. Sometimes the motor will have a sluggish start and not pop the circuit breaker, but will not spin fast enough to engage the internal centrifugal run switch. Often this may be due to other devices on the same circuit breaker and you can't draw maximum current. The reason the breaker does not pop is varied. The breaker is a slow reacting type, the breaker is old and it too is sluggish, possible loose connections inside the outlet such as a loose neutral, and then you may just have lazy electrons.

If this is a belt driven saw, perhaps the belt tension is too tight. I have a Jet table saw and by adjusting the belt tension incorrectly I can emulate your challenge.

A) If you have a duplex (2 in 1) receptacle try plugging in a work light or a small table lamp. Then try starting your table saw, but unless it starts up and runs switch it off fast. Did the light really dim? If yes, then please try step 2.

B) Try plugging it into another receptacle and if possible one that's on a different circuit. Did anything change.

C) Do be sure the belt isn't overly tightened. With the plug pulled for safety, how does it feel if you pull on the belt and try to spin the saw blade and motor by hand?

And finally remove the belt, plug the saw back in and power up the motor but be ready to switch off power fast in case things go wrong. Do brace the motor so it can't freely move about. Put simple you may need a way to hold the motor in position. I don't have this table saw so I'm not sure how the motor mounting works. The test is to see if with the belt off does the motor quickly start and come up to speed or not.

Please report the test results.

Comment

Well, I tried plugging into a different outlet and circuit but it didn't help. I even tapped it with a rubber mallet. I blew it out and this didn't help. It did get a little better but it just starts out and goes slow. Anymore advice?

Comment

Just as it is right now, be sure the plug is pulled and try manually pulling on the belt. Does everything spin freely or is there much resistance? A little resistance is normal but you shouldn't need to pull hard to move the motor and blade forward and backward.

Next please try removing the belt and then see how it starts and runs, but first manually spin the motor. Is there much force required to spin it by hand with the belt off? If yes, STOP and figure something is wrong with the motor. If it's pretty easy to manually spin the motor then carefully try powering it up with the belt off. It should start and come to speed fast. If it seems sluggish you may as well figure that the motor needs repairs. Carefully noting the wiring connections (most likely quick connectors that push on and pull off) disconnect it and remove the mounting bolts. Then with the motor free take it to a electric motor repair shop.

Has anyone touched any of the wiring since you got the saw home? Did it ever run with good power?

One thing that hasn't yet been brought up is that bad ball bearings can bog down a motor. This is where a test with the belt off will give good clues. With it up and running and the power switched flipped to off it should take awhile to coast to a stop. Sometimes the arbor bearings go bad so a manual spin of the blade can clue you in as well. It should feel smooth and turn with little resistance.

Comment

a final thought, get a voltmeter and measure the AC voltage at your outlet.
You should see 120VAC. If you see anything less you may have other issues.
Now if you see say 115-125V or measure the 240 line and see say 237-245 you are ok and in a reasonable range.

It's not unlikely for you to read different power line values. A low voltage will effect the motor. If you're using an extension cord then you have added an entire new range of challenges! If you are using a 14 or 16 gauge extension cord, no matter how short it may be, you could have a voltage drop and the motor won't run correctly.

If you do require an extension cord keep it as short as reasonable and use at a minimum a 12 gauge or better yet a 10 gauge extension cord.

Returning to the motor itself, as others have told you if indeed the motor without any load acts weird take it to a motor repair place. they can check it out on a growler and determine if you may have some defective windings.

Cactus Man

Comment

Thanks to everyone for the advice. I have tried everything and nothing has helped. I even bypassed the switch. I called the authorized Rigid repair person and he is ordering me a new motor. The serial number showed the saw was less than 3 years old so I won't be responsible for the repair but just out of curiosity I looked to see how much a new motor would be and it was $574! Ridiculous that I could buy a whole new saw for that much. Hopefully I'll be back to cutting a week or so.